Re-enable TLS version negotiation by default

Re-enable TLS version negotiation by default

Re-enable TLS version negotiation by default, so that users
benefit from the stronger and better crypto of TLSv1.1 and
TLSv1.2, without having to add 'tls-version-min' to their
config files.

We tried this before in 2.3.3, but got various reports of people
no longer being able to connect.  Back then, we did not have a
way for users to control the TLS version.  We now have
--tls-version-min and --tls-version-max, and even automatically
set --tls-version-max to 1.1 if --cryptoapi is used, because
the cryptoapi code is incompatible with TLS 1.2.

To make sure users can fall back to the _exact_ old default
behaviour, not only limit the TLS version to 1.0 if
--tls-version-max 1.0 is set, but also keep using the API calls
TLSv1_{client,server}_method(), instead of the ones that support
negotiation (SSLv23_{client,server}_method()).  (Yes, the naming
is awkward, but 'SSLv23' really means 'enable negotiation' in
OpenSSL-API language.

This patch is for the release/2.3 branch only.

Signed-off-by: Steffan Karger <steffan@karger.me>
Acked-by: Matthias Andree <matthias.andree@gmx.de>
Message-Id: <1426015605-4068-1-git-send-email-steffan@karger.me>
URL: http://article.gmane.org/gmane.network.openvpn.devel/9542
Signed-off-by: Gert Doering <gert@greenie.muc.de>